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+'\" et
+.TH SIGALTSTACK "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
+.SH PROLOG
+This manual page is part of the POSIX Programmer's Manual.
+The Linux implementation of this interface may differ (consult
+the corresponding Linux manual page for details of Linux behavior),
+or the interface may not be implemented on Linux.
+
+.SH NAME
+sigaltstack
+\(em set and get signal alternate stack context
+.SH SYNOPSIS
+.LP
+.nf
+#include <signal.h>
+.P
+int sigaltstack(const stack_t *restrict \fIss\fP, stack_t *restrict \fIoss\fP);
+.fi
+.SH DESCRIPTION
+The
+\fIsigaltstack\fR()
+function allows a process to define and examine the state of an
+alternate stack for signal handlers for the current thread. Signals
+that have been explicitly declared to execute on the alternate stack
+shall be delivered on the alternate stack.
+.P
+If
+.IR ss
+is not a null pointer, it points to a
+.BR stack_t
+structure that specifies the alternate signal stack that shall take
+effect upon return from
+\fIsigaltstack\fR().
+The
+.IR ss_flags
+member specifies the new stack state. If it is set to SS_DISABLE, the
+stack is disabled and
+.IR ss_sp
+and
+.IR ss_size
+are ignored. Otherwise, the stack shall be enabled, and the
+.IR ss_sp
+and
+.IR ss_size
+members specify the new address and size of the stack.
+.P
+The range of addresses starting at
+.IR ss_sp
+up to but not including
+.IR ss_sp +\c
+.IR ss_size
+is available to the implementation for use as the stack. This function
+makes no assumptions regarding which end is the stack base and in which
+direction the stack grows as items are pushed.
+.P
+If
+.IR oss
+is not a null pointer, upon successful completion it shall point to a
+.BR stack_t
+structure that specifies the alternate signal stack that was in effect
+prior to the call to
+\fIsigaltstack\fR().
+The
+.IR ss_sp
+and
+.IR ss_size
+members specify the address and size of that stack. The
+.IR ss_flags
+member specifies the stack's state, and may contain one of the
+following values:
+.IP SS_ONSTACK 12
+The process is currently executing on the alternate signal stack.
+Attempts to modify the alternate signal stack while the process is
+executing on it fail. This flag shall not be modified by processes.
+.IP SS_DISABLE 12
+The alternate signal stack is currently disabled.
+.P
+The value SIGSTKSZ is a system default specifying the number of bytes
+that would be used to cover the usual case when manually allocating an
+alternate stack area. The value MINSIGSTKSZ is defined to be the
+minimum stack size for
+a signal handler. In computing an alternate stack size, a program
+should add that amount to its stack requirements to allow for the
+system implementation overhead. The constants SS_ONSTACK, SS_DISABLE,
+SIGSTKSZ, and MINSIGSTKSZ are
+defined in
+.IR <signal.h> .
+.P
+After a successful call to one of the
+.IR exec
+functions, there are no alternate signal stacks in the new process
+image.
+.P
+In some implementations, a signal (whether or not indicated to execute
+on the alternate stack) shall always execute on the alternate stack if
+it is delivered while another signal is being caught using the
+alternate stack.
+.P
+Use of this function by library threads that are not bound to
+kernel-scheduled entities results in undefined behavior.
+.SH "RETURN VALUE"
+Upon successful completion,
+\fIsigaltstack\fR()
+shall return 0; otherwise, it shall return \(mi1 and set
+.IR errno
+to indicate the error.
+.SH ERRORS
+The
+\fIsigaltstack\fR()
+function shall fail if:
+.TP
+.BR EINVAL
+The
+.IR ss
+argument is not a null pointer, and the
+.IR ss_flags
+member pointed to by
+.IR ss
+contains flags other than SS_DISABLE.
+.TP
+.BR ENOMEM
+The size of the alternate stack area is less than MINSIGSTKSZ.
+.TP
+.BR EPERM
+An attempt was made to modify an active stack.
+.LP
+.IR "The following sections are informative."
+.SH EXAMPLES
+.SS "Allocating Memory for an Alternate Stack"
+.P
+The following example illustrates a method for allocating memory for an
+alternate stack.
+.sp
+.RS 4
+.nf
+\fB
+#include <signal.h>
+\&...
+if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
+    /* Error return. */
+sigstk.ss_size = SIGSTKSZ;
+sigstk.ss_flags = 0;
+if (sigaltstack(&sigstk,(stack_t *)0) < 0)
+    perror("sigaltstack");
+.fi \fR
+.P
+.RE
+.SH "APPLICATION USAGE"
+On some implementations, stack space is automatically extended as
+needed. On those implementations, automatic extension is typically not
+available for an alternate stack. If the stack overflows, the
+behavior is undefined.
+.SH RATIONALE
+None.
+.SH "FUTURE DIRECTIONS"
+None.
+.SH "SEE ALSO"
+.IR "Section 2.4" ", " "Signal Concepts",
+.IR "\fIexec\fR\^",
+.IR "\fIsigaction\fR\^(\|)",
+.IR "\fIsigsetjmp\fR\^(\|)"
+.P
+The Base Definitions volume of POSIX.1\(hy2008,
+.IR "\fB<signal.h>\fP"
+.SH COPYRIGHT
+Portions of this text are reprinted and reproduced in electronic form
+from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
+-- Portable Operating System Interface (POSIX), The Open Group Base
+Specifications Issue 7, Copyright (C) 2013 by the Institute of
+Electrical and Electronics Engineers, Inc and The Open Group.
+(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
+event of any discrepancy between this version and the original IEEE and
+The Open Group Standard, the original IEEE and The Open Group Standard
+is the referee document. The original Standard can be obtained online at
+http://www.unix.org/online.html .
+
+Any typographical or formatting errors that appear
+in this page are most likely
+to have been introduced during the conversion of the source files to
+man page format. To report such errors, see
+https://www.kernel.org/doc/man-pages/reporting_bugs.html .